(a) Field of the Invention
This invention relates to a process for producing a gaseous mixture containing hydrogen and carbon monoxide in which sulfur containing hydrocarbon is directly subjected to steam reforming without being desulfurized in advance, and also relates to an apparatus therefor.
(b) Description of the Prior Art
Sulfur containing hydrocarbon, particularly extracted oil such as kerosene, gas oil, vacuum distillation gas oil and the like, obtained by subjecting petroleum to atmospheric distillation and vacuum distillation, contains a considerable amount of sulfur, for example, 40 to 100 ppm for commercially available desulfurized kerosene, 200 to 1,500 ppm for gas oil, and more for vacuum distillation gas oil. Accordingly, this sulfur containing hydrocarbon is unable to be subjected directly to steam reforming in the presence of the conventional nickel containing catalyst.
The technical problems to be solved in a process for steam reforming, in which light hydrocarbon such as butane and naphtha is subjected to steam reforming with an oxidizing agent for reforming such as steam at a high temperature of from 500.degree. to 850.degree. C. in the presence of a nickel containing catalyst, consist in maintenance of the activity of the nickel containing catalyst and prevention of carbon deposition on the catalyst, and many conventional processes therefor have been proposed so far and have been brought into industrial practice. However, all the conventional processes of steam reforming mentioned above have such drawback that light hydrocarbons as raw material must be subjected to desulfurization in advance so that sulfur may substantially be removed. Sulfur contained in a raw material converts nickel in the catalyst to nickel sulfide, whereby the activity of the catalyst is lost and deposition of carbon is caused, which makes a long-run operation impossible. As the sulfur content in the raw material is increased, troubles due thereto are increased.
There is a description regarding the above at page 69 of an article titled by "Production of Hydrogen Naphtha Steam Reforming" beginning at page 66, No. 10, Vol. 21, "Petroleum & Petrochemistry", which states as follows: "A complete steam reforming of light gas oil (LBP/FBP=134.degree. C./314.degree. C.) by the use of a laboratory apparatus under the same conditions as in the production of ammonia synthesis gas is attained. However, the insufficient desulfurization (20 ppm) of the raw material causes to poison the catalyst, and 2 to 3 hours later a part of the raw material is not subjected to reforming and leaves the catalyst bed as it is to be contained in outlet gas." Clearly, the above description shows that even 20 ppm of sulfur cause to lose the activity of the catalyst within a short period of time of 2 to 3 hours. Accordingly, the raw material must be subjected to a desulfurization process such as hydrodesulfurization in advance so that the sulfur content in the raw material may be less than 1 ppm, preferably less than 0.1 ppm before being subjected to steam reforming in order to make possible to long-run operation.
Most of sulfur compounds contained in a light fraction such as naphtha are generally thiols and sulfides, and the sulfur moiety thereof can more readily be removed by hydrodesulfurization. However, sulfur compounds contained in a heavy fraction such as kerosene are mainly thiophenes, which are extremely difficult to be desulfurized by hydrodesulfurization from technical and economical viewpoints.
As mentioned above, the conventional processes for high temperature steam reforming of hydrocarbon by use of a nickel containing catalyst have a drawback that sulfur in the raw material must be removed in advance, but desulfurization of heavy fractions is difficult technically as well as economically. Therefore the raw materials containing such heavy fractions are unable to be subjected to steam reforming.
With respect to chemical raw material, an emphasis must be put on the saving of resources, and application of heavier and diversified raw material taking the future shortage of petroleum resources into consideration. Accordingly, developments of a process for hydrocarbon steam reforming and an apparatus therefor are highly demanded, in which heavy fractions obtained by removing atmospheric and vacuum distillation residue of petroleum can be widely used as raw materials, and sulfur containing material can also be used without need to be desulfurized in advance.